my answer C

clock60 wrote:Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time they have introduced some 100,000 dangerous chemical pollutants, having gone virtually unregulated since they were developed more than 50 years ago.

a)while at the same time they have introduced some 100,000 dangerous chemical pollutants, having
b)while at the same time introducing some 100,000 dangerous chemical pollutants that have
c)while they have introduced 100,000 dangerous chemical pollutants at the same time, and have
d)but introducing some 100,000 dangerous chemical pollutants at the same time that have
e)but at the same time introduce some 100,000 dangerous chemical pollutants, having

Just memorize one thing:

While at the same time + VERBING is most often used in GMAT. I have seen in GMATPREP sentences. GMAT is a fan of this uses. If you study at least 100 sentences from GMATPREP and make your note by analyzing the patterns of the sentences GMAT likes, I am sure your SC skill will improve dramatically.

Ok, come to the point.

Just by looking the "while at the same time + Verbing", you can guess the answer, but you MUST check other options as well.

Industrialization and modern methods have improved ....pollutants, having gone

The problems in this sentence:

COMMA + Verbing" modifies the entire preceding clause, and the subject of the preceding clause becomes the subject of the VERBING.

Now, A means that "Industrialization and modern methods have gone unregulated". This is changing the intended meaning of the sentence. E is also in this category.

COMMA + AND + VERB: is correct only when we use a list of more than two verbs, and we should use "COMMA + AND VERB" at last. This kills C.

BUT INTRODUCING is not parallel with any one of the previous verb. This kills D.

They are not going to NY but are going to LA.

Answer is B.

the above looks like perfect solving, oa is B
thank you gmat_perfect

5abi, Option C is incorrect because:

>> "and have" at the last is pointing to the "industrialization and modern methods". It should instead point to chemical pollutants.

Thus, B is correct.

I hope this explanation is clear to you.

5abi wrote:my answer C